Conventionally, many materials obtained by various molding methods are used as a skin for vehicle internal parts. These materials and methods include for example, vacuum molding of polyvinyl chloride (PVC), vacuum molding and powder molded articles using thermal plastic olefins (TPO), or slush molded articles of thermal plastic polyurethane (TPU), articles produced by spraying polyurethane material (polyurethane liquid mixtures mixed by collision under high pressure of a polyol and an isocyanate) and articles molded using RIM (Reaction Injection Molding).
Generally methods for producing a laminate using a core material or an integral skin molded article comprising a cushioning material such as a skin formed as described above and polyurethane foam for example include setting a skin and a core material pre-placed in a mold for heating or vacuum molding in order to set in the mold and then injecting polyurethane as a cushioning material between the skin and the core material or a method of adhesive molding in which an adhesive is applied.
However, these methods for producing a laminate using a core material or an integral skin molded article require two molding steps and therefore complicate product processing with respect to equipment or the like, increase production time, increase costs and thus adversely affect productivity.
Furthermore, there are respectively some shortcomings in the materials used for the skin up until now. PVC materials produce dioxin or chlorinated byproducts when decomposed and therefore have an adverse effect on the environment. In addition, disposal and recycling is difficult and therefore such materials are considered not to be preferred.
Vacuumed-molded articles using TPO are not suitable since they are hard to the touch. Powder molded articles require a large amount of energy and time in the molding process and therefore similar to PVC are associated with low efficiency production and therefore are not economic.
Although articles which are slush molded using TPU have improved tactile characteristics, they require large amounts of energy and time in processing, are associated with low efficiency production and therefore are not economic.
Instead of conventionally used TPU slush molding, articles which employ spraying of polyurethane material in order to improve productivity generally attempt to increase productivity by using highly reactive materials. However since dispersal of materials during the spray processing is prohibited, time is required since it is necessary to eliminate dispersed materials from around the mold. Thus the time required to eliminate dispersed material often causes a reduction in productivity. Furthermore the use of materials is higher than the required amount due to the prohibition on dispersal of materials. This therefore increases costs, adversely affects the working environment and thus is not preferred.
Polyurethane materials in the spray used in methods of spraying are liable to be affected by humidity or the surrounding temperature and tend to produce foam as a result of moisture in the air or air in air bubbles in the article. Furthermore the molding of articles for internal parts of large vehicles require spraying of the mold on a number of occasions. Consequently layers of differing density or hardness tend to be generated at the interface regions before and after blasting of polyurethane material. This tendency results in undesirable surface tactile characteristics. For these reasons, there are drawbacks with respect to a lack of uniform tactile characteristics resulting from the density of the skin, that is to say, the thickness or hardness.
Since RIM molded articles using polyurethane materials faithfully reproduce surface irregularities, a superior outer design appearance can be achieved. In addition, since the internal die capacity is fixed, these methods have the advantage of stable density, thickness or hardness and therefore have been applied in a wide range of applications. The thickness of the skin used in the design surfaces of vehicle internal parts is generally approximately from 0.5 mm to 3.0 mm and is generally thicker than RIM molded articles. Consequently flow resistance increases and it is necessary to delay the reaction to an extent in order to fill up to the extremities of the article. As a result, curing time (the time from injection of polyurethane materials into the die up to the commencement of die opening) increases and productivity is adversely affected.
Vehicle internal parts with a skin for example instrument panels or door trim on which a skin is used on the design face, and in particular, an automobile instrument panel, naturally require physical characteristics such as UV stability, anti-wear characteristics, airbag expansion characteristics, durability but also require a skin satisfying quality outer appearance and tactile characteristics. Therefore there is a need for a method of preparing which integrally molds an integral skin molded article comprising semi-hard polyurethane foam in order to soften shocks with the design surface skin, or a laminate comprising a core material which retains the integral skin molded article. The method should reduce cycle times improve productivity with respect to use of materials and reduce production costs.
There is a need for articles and a method of preparing such articles such as vehicle internal parts, in particular for a skin for internal automobile parts, which improves productivity and reduces production costs. There have been several proposals made up to date.
Japanese Unexamined Patent Publication (Kokai) No. 52-142797 discloses a method of preparing a polyurethane flexible molded article using a specific polyol and a specific aromatic diamine. The method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 52-142797 proposes the molding in a short time of a polyurethane flexible body using a specific polyol and a specific aromatic diamine. However the molded article has a weight of 3 to 10 kg or more and is directed to large externally mounted articles, for example, bumper bars. The examples of Japanese Unexamined Patent Publication (Kokai) No. 52-142797 disclose a molded article which has a thickness of 4 mm and which is comparatively hard with a Shore hardness of 84 or more. However, the skin of this disclosure can not be used in the design surface of vehicle internal parts.
Japanese Unexamined Patent Publication (Kokai) No. 53-86763 discloses a method of forming a foam layer by molding a skin using reaction injection molding of a polyurethane material in a die cavity, leaving the skin in the die and setting a second core die capable of forming a cavity corresponding to the thickness of a foam layer instead of removing the first core die. A foam layer which tightly adheres to the skin is formed by injecting a foam molding material into the cavity. The method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 53-86763 proposes a method of integrally forming internal articles with a skin. However the disclosure is only related to a urethane skin material and detailed description of a urethane composition, urethane density or surface hardness related to the present method is not provided and therefore is not sufficient.
Japanese Unexamined Patent Publication (Kokai) No. 2003-19056 discloses a seat cushion using a seamless skin material and a method of preparing same. The method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2003-19056 proposes a seat cushion formed from a foam body having a shape approximately corresponding to the border of the seat cushion and a seamless skin material which is tightly and integrally adhered to the surface and side faces of the foam body. However this disclosure is only related to a urethane skin material and detailed description of a urethane composition, urethane density or surface hardness related to the present production method is not provided and therefore is not sufficient.    [Patent Document 1] Japanese Unexamined Patent Publication (Kokai) No. 52-142797    [Patent Document 2] Japanese Unexamined Patent Publication (Kokai) No. 53-86763    [Patent Document 3] Japanese Unexamined Patent Publication (Kokai) No. 2003-19056
Thus with respect to integral skin molded articles formed from high density polyurethane resin and polyurethane foam, there is no current solution to the need for a method of forming a skin having a superior external appearance, an integral skin molded article using the skin and a laminate with a skin laminated using a core material which reduces production costs and improves productivity.